The present invention relates generally to tank pressure management systems, and more particularly to systems and methods for managing pressure in storage tanks.
As is known in the art, filling stations allow people to dispense fuel from underground storage tanks through nozzles to a vehicle tank. Absent vapor recovery systems, vapor from the vehicle tank and/or fueling operation typically escapes into the atmosphere as the vapor is displaced by liquid gasoline.
To solve the problem of vapor loss at the nozzle, xe2x80x9cStage IIxe2x80x9d vapor recovery systems were implemented. More specifically, gasoline dispensing nozzles were provided with vapor recovery systems to lessen the amount of vapor that might escape into the atmosphere when liquid is displaced. One such system is known as the xe2x80x9cbalancexe2x80x9d vapor recovery system and provides a rubber boot which surrounds the dispensing nozzle and extends to form a seal with the fill pipe of the automobile tank. Vapor from the automobile tank is collected and flows through the rubber boot to the storage tank.
Another common Stage II vapor recovery system utilized by dispensing nozzles includes the xe2x80x9cvacuum assistxe2x80x9d vapor recovery system. Such systems utilize a vacuum pump to collect vapor from the automobile tank through passageways in the nozzle and return the removed vapor to the storage tank.
While the Stage II vapor recovery systems addressed some of the problems found in the art, it was subsequently discovered that such systems can disadvantageously pressurize the storage tanks where more vapor is being returned to the storage tank than gasoline dispensed to the automobile fuel tank. As a result, onboard refueling vapor recovery (ORVR) vehicles were developed to prevent the escape of vapor from the vehicle gasoline tank. It was discovered, however, that Stage II vapor recovery systems, rather than collecting vapor from an ORVR vehicle, would collect fresh air, thus recreating the problem of storage tank pressurization. Therefore, with the onset of the ORVR vehicles, there is now a more urgent need to ensure that the coexistence of the two vapor recovery systems (ORVR and Stage II) do not create greater emissions than before (when only Stage II was present) as a result of overpressure in the storage tanks.
Initially, Stage II vapor recovery systems were adapted to slow or stop Stage II vapor recovery in the presence of an ORVR vehicle. Stage II systems accomplished this by providing various sensors for sensing the presence of an ORVR vehicle and adjusting the recovery of vapor accordingly. While such Stage II sensors were effective in slowing or stopping vapor recovery from an ORVR vehicle, problems still existed when there were no vehicles dispensing fuel as Stage II systems maintain tank pressure through exchange of gasoline and vapor with vehicle gasoline tanks. Thus, without dispensing fuel into vehicles, the natural evaporative behavior of gasoline pressurizes the storage tank (e.g. as a result of higher temperatures or just the natural tendency of hydrocarbon liquids to vaporize). To solve this problem, further systems were developed for managing storage tank pressure.
Most recently, systems utilizing high tech xe2x80x9cmembrane technologyxe2x80x9d have been introduced to manage pressure in storage tanks. For example, in U.S. Pat. No. 5,464,466 to Gilbarco, a pump recirculates vapor from a storage tank through a membrane that separates clean air from hydrocarbon vapor, with clean air being exhausted to the atmosphere and hydrocarbon vapor being returned to the tank.
Another system utilizing xe2x80x9cmembrane technologyxe2x80x9d includes applicants own system known as the Vaporsaver System. The Vaporsaver System condenses the vapor from the storage tank to yield liquid gasoline and then filters the remaining hydrocarbon vapor through a membrane. Upon separation and membrane filtration, liquid gasoline and saturated vapor are returned to the storage tank and clean air is released into the atmosphere.
The present invention addresses certain issues with systems employing xe2x80x9cmembrane technology.xe2x80x9d First, the present invention recognizes that the membranes of the aforementioned systems may fail, potentially leading to the release of dangerous hydrocarbon vapor into the environment. Moreover, with the present invention it is possible to manage tank pressure without releasing any air or vapor into the environment.
Another issue readdressed by the present invention is that the membranes utilized in xe2x80x9cmembrane technologyxe2x80x9d eventually wear out and need to be replaced. Replacement of membranes can be expensive, and if not done properly or timely, can result in undesirable emissions. In addition, replacement of membranes requires that the tank pressure management system be shut down during replacement, thus potentially allowing the pressure in the tank to increase. If the pressure in the tank increases beyond that of atmospheric pressure, leaks or releases that the pressure management system seeks to prevent may occur.
Thus, while systems employing membrane technology are certainly helpful for managing pressure in a storage tank, there is still room for enhancing tank pressure management systems with improved properties. Accordingly, there is a desire to manage tank pressure in an efficient, cost effective manner without use of membranes and/or in addition to such membranes.
Accordingly, the present invention is intended to address and obviate problems and shortcomings and otherwise improve previous tank pressure management systems. More particularly, it is one object of the present invention to provide closed systems and methods for managing pressure in storage tanks.
To achieve the foregoing and other objects in accordance with exemplary embodiments of the present invention, tank pressure management systems comprise a vapor condensing system in fluid communication with a storage tank and an accumulator vessel in fluid communication with the vapor condensing system and a storage tank. In one embodiment, the accumulator vessel includes an air/vapor outlet and a liquid outlet, wherein an air/vapor conduit connects the air/vapor outlet of the accumulator vessel with a storage tank and a liquid conduit connects the liquid outlet of the accumulator vessel with a storage tank. As such, the tank pressure management system of the current invention provides a closed system for condensing liquid gasoline from air/vapor to reduce tank pressure and returning all air, vapor and liquid to a storage tank without a need for emission of air or vapor into the atmosphere.
To still further achieve the foregoing and other objects in accordance with exemplary embodiments of the present invention, a method of managing air/vapor pressure of a storage tank is provided comprising the steps of monitoring the pressure in a storage tank, removing air/vapor from said storage tank when the monitored pressure reaches a first preset level, separating liquid from the air/vapor, returning all remaining air/vapor to a storage tank and returning the separated liquid to a storage tank. Therefore, there is provided a method for condensing liquid gasoline from air/vapor to reduce tank pressure and returning all air, vapor and liquid to a storage tank without emission of air or vapor into the atmosphere.
Still other embodiments, combinations, advantages and objects of the present invention will become apparent to those skilled in the art from the following description wherein there are shown and described alternate exemplary embodiments of this invention for illustration purposes. As will be realized, the invention is capable of other different aspects, objects and embodiments, all without departing from the scope of the invention. Accordingly, the drawings, objects, and descriptions should be regarded as illustrative and exemplary in nature only, and not as restrictive.